Setting HttpClient to a too short timeout crashes process

Question

I've noticed that when I'm using System.Net.HttpClient with a short timeout, it may sometimes crash the process, even when it is wrapped in a try-catch block. Here's a short program to reproduce this.

public static void Main(string[] args) {     var tasks = new List<Task>();     for (int i = 0; i < 1000; i++)     {         tasks.Add(MakeHttpClientRequest());     }     Task.WaitAll(tasks.ToArray());  }  private async static Task MakeHttpClientRequest() {                 var httpClient = new HttpClient { Timeout = TimeSpan.FromMilliseconds(1) };     var request = "whatever";     try     {         HttpResponseMessage result =             await httpClient.PostAsync("http://www.flickr.com/services/rest/?method=flickr.test.echo&format=json&api_key=766c0ac7802d55314fa980727f747710",                                  new StringContent(request));                      await result.Content.ReadAsStringAsync();                     }     catch (Exception x)     {         Console.WriteLine("Error occurred but it is swallowed: " + x);     } } 

Running this will crash the process with the following exception:

Unhandled Exception: System.AggregateException: One or more errors occurred. ---> System.Net.WebException: The request was canceled    at System.Net.ServicePointManager.FindServicePoint(Uri address, IWebProxy proxy, ProxyChain& chain, HttpAbortDelegate& abortDelegate, Int32& abortState)    at System.Net.HttpWebRequest.FindServicePoint(Boolean forceFind)    at System.Net.HttpWebRequest.get_ServicePoint()    at System.Net.AuthenticationState.PrepareState(HttpWebRequest httpWebRequest)    at System.Net.AuthenticationState.ClearSession(HttpWebRequest httpWebRequest)    at System.Net.HttpWebRequest.ClearAuthenticatedConnectionResources()    at System.Net.HttpWebRequest.Abort(Exception exception, Int32 abortState)    at System.Net.HttpWebRequest.Abort()    at System.Net.Http.HttpClientHandler.OnCancel(Object state)    at System.Threading.CancellationCallbackInfo.ExecutionContextCallback(Object obj)    at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)    at System.Threading.CancellationCallbackInfo.ExecuteCallback()    at System.Threading.CancellationTokenSource.CancellationCallbackCoreWork(CancellationCallbackCoreWorkArguments args)    at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)    --- End of inner exception stack trace ---    at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)    at System.Threading.CancellationTokenSource.NotifyCancellation(Boolean throwOnFirstException)    at System.Threading.CancellationTokenSource.TimerCallbackLogic(Object obj)    at System.Threading.TimerQueueTimer.CallCallbackInContext(Object state)    at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)    at System.Threading.TimerQueueTimer.CallCallback()    at System.Threading.TimerQueueTimer.Fire()    at System.Threading.TimerQueue.FireNextTimers()    at System.Threading.TimerQueue.AppDomainTimerCallback() 

Digging in a little, it seems that when HttpClient aborts the request before a relevant ServicePoint is created, HttpWebRequest attempts to create the ServicePoint, via ServicePointManager.FindServicePoint, which throws a RequestCanceled. Since this exception is thrown in the thread that attempts to cancel the request, it is not caught, and the process dies.

Am I missing something? Have you run into this issue?

Answer 1

HttpWebRequest.Abort() is throwing an exception on a background/timer thread. This has nothing to do with HttpClient's Task management.

The exception from HttpWebRequest.Abort() should be fixed in .NET 4.5 GDR1. http://support.microsoft.com/kb/2750149 http://support.microsoft.com/kb/2750147